For some reason, every time I start up the DX10 ver it starts in window mode by default, even after I change it in the game. The weird thing is that I initially just get black screen and the game won't load any further. But I found a simple fix: alt tab out, then try to close the window and bingo... the game starts. Silly but it works.

Yep it's the same here. It starts windowed from time to time on Vista64 and dx10. I have several starts with black screen too, but I close the demo from the taskbar and start it again. Weird ! Hope they fix it for the final game.